1. Technical Field of the Invention
The present invention relates generally to the field of image acquisition. More specifically, the present invention relates to systems and methods for obtaining and processing images of fingerprints for navigation and recognition purposes.
2. Description of Related Art
The use of fingerprints for identification purposes can be dated back for centuries. For example, in 14th century Persia, various official government papers included fingerprints (impressions), and one government official observed that no two fingerprints were exactly alike. In recent times, fingerprints play an important role in what is known as biometrics, which refers to the identification of an individual based on his or her physiological or behavioral characteristics. Biometrics enables automatic personal identification for a number of applications, such as criminal investigations, physical access to facilities and electronic access to computers and/or data on computer systems.
Fingerprints can now be acquired directly in the form of a digital image, without the need for an intermediate step of obtaining an impression of the fingerprint on paper, as was traditionally done. Digital fingerprints can be stored and processed in subsequent fingerprint enhancing and fingerprint matching applications. In order to capture a fingerprint image with enough features for recognition, a certain resolution and finger tip area are required. For example, the Federal Bureau of Investigations (FBI) recommends a 12×16 mm finger tip area, with 400 dpi resolution. In other applications where size and cost are important factors, smaller finger tip areas, with the same or lower resolutions, can be used. For example, a 9×12 mm finger tip area, with a resolution as low as 300 dpi, has been used in many applications. However, in smaller area and/or lower resolution fingerprint imaging applications, the finger-recognition algorithmic performance is usually inferior due to the reduction in the number of captured features.
For some applications, dedicating an area of even 9×12 mm to capture a fingerprint image is undesirable. For example, in the design of cell phones, laptop computers, personal digital assistants, electronic mice and other electronic devices, there is a trend towards miniaturization of the device itself, while at the same time offering more features. Therefore, in order to provide finger recognition capabilities on such electronic devices, the sensing area needs to be as small as possible. However, there is not currently a fingerprint scanner available that has a small enough sensing area for implementation on such electronic devices, while still enabling adequate finger-recognition algorithmic performance.
Another feature many electronic devices also provide is a navigation mechanism for controlling a cursor or pointer on a screen. By far, the most popular navigation mechanism in PC usage is the mouse. Recently, optical mice have been developed that are able to navigate on nearly any arbitrary surface using a tracking algorithm that correlates sequential images in the direction of movement. For example, U.S. Pat. No. 6,281,882, entitled PROXIMITY DETECTOR FOR A SEEING EYE MOUSE, which is hereby incorporated by reference in its entirety, describes an optical mouse that images the spatial features of a surface below the mouse and compares successive images to ascertain the direction and amount of movement. In addition, as described in U.S. Pat. No. 6,057,540, entitled MOUSELESS OPTICAL AND POSITION TRANSLATION TYPE SCREEN POINTER CONTROL FOR A COMPUTER SYSTEM, which is hereby incorporated by reference in its entirety, an optical finger navigation device has also been developed that detects motion of the finger and translates the finger motion into corresponding motion of the cursor or pointer on the screen.
Placing separate sensing areas for finger recognition and finger navigation on the same electronic device is inefficient from both a cost perspective and a space perspective. However, there is not currently a fingerprint scanner available capable of performing both finger recognition and finger navigation. Therefore, what is needed is an optical mechanism of combining finger recognition and finger navigation using a single sensing area of a size sufficiently small for integration with electronic devices. In addition, what is needed is a cost-effective imaging system capable of performing both finger recognition and finger navigation, while minimizing power consumption and space required on small and/or portable electronic devices.